Atherosclerotic Aortic Gangliosides Enhance Integrin-Mediated Platelet Adhesion to Collagen

Abstract

Abstract —Gangliosides, sialic acid–containing glycosphingolipids, accumulate in atherosclerotic vessels. Their role in the pathogenesis of atherosclerosis is unknown. Gangliosides isolated from tumor cells promote collagen-stimulated platelet aggregation and ATP secretion and enhance platelet adhesion to immobilized collagen. These activities are all mediated by ganglioside effects on the platelet integrin collagen receptor α 2 β 1 . Therefore, we hypothesized that gangliosides isolated from atherosclerotic plaques would enhance platelet adhesion to immobilized collagen, a major component of the subendothelial matrix of blood vessels. Furthermore, we questioned whether this effect of atherosclerotic gangliosides might play a role in the pathogenesis of atherosclerosis. To test this hypothesis, we isolated the gangliosides from postmortem aortas of patients with extensive atherosclerotic disease and examined their effects on platelet adhesion. Samples of aortic tissue taken from areas involved with atherosclerotic plaque demonstrated accumulation of gangliosides (64.9±6.5 nmol/g wet weight) compared with gangliosides isolated from control normal aortic tissue taken from children who died of noncardiac causes (NAGs; 21.1±6.4 nmol/g wet weight). Interestingly, samples of tissue taken from diseased aortas but from areas not involved with gross plaque formation also demonstrated ganglioside accumulation (47.6±12.8 nmol/g wet weight). Next, the activity of each of these gangliosides on platelet adhesion to immobilized type I collagen was studied. Atherosclerotic aortic gangliosides (AAGs) as well as those isolated from grossly unaffected areas of the same aorta (UAGs) both increased platelet adhesion compared with control NAGs (OD 570 , 0.37±0.11 and 0.29±0.14 versus 0.16±0.07, respectively; P <0.01 and P <0.05, respectively). These OD 570 values corresponded to 9×10 5 , 8×10 4 , and 6×10 3 platelets per well after preincubation with 5 μmol/L AAG, UAG, and NAG, respectively. Increased adhesion was observed after preincubation with as little as 0.5 μmol/L AAG, and maximal adhesion was seen at 2.5 μmol/L, with a plateau extending to the highest concentration tested, 10 μmol/L. The effect of AAGs on platelet adhesion to collagen was abrogated by incubation of treated platelets with F-17 anti-α 2 monoclonal antibody (OD 570 , 0.13±0.02). Finally, the effects of the major individual gangliosides isolated from atherosclerotic tissues, G M3 and G D3 , were tested. G M3 increased adhesion to collagen (OD 570 , 0.415±0.06) as did G D3 (0.31±0.08). Similar to that of AAGs, the effect of both molecules was blocked by F-17 (0.09±0.04 and 0.13±0.06, respectively). These experiments demonstrate that accumulated atherosclerotic gangliosides promote platelet adhesion to collagen, the major component of the subendothelial matrix. Furthermore, this activity is mediated by an effect of the gangliosides on the collagen-binding integrin α 2 β 1 . This activity may provide a mechanism for the development of platelet thrombi at sites where atherosclerotic gangliosides accumulate and help to explain the role of platelets in the process of atherosclerotic disease progression.